linux-kernel - Re: RFC: running out of x86 boot loader IDs

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Date:	Fri, 30 Jan 2009 01:33:28 +0100
From:	Mikael Pettersson <mikpe@...uu.se>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org
Subject: Re: RFC: running out of x86 boot loader IDs

H. Peter Anvin writes:
 > The 4-bit values used to hold x86 boot loader IDs are near exhaustion. 
 > As a result, I'm proposing an extension protocol and will implement it 
 > in time for the next merge window unless there are objections.
 > 
 > The proposal will be as follows:
 > 
 > - The boot loader IDs (type_of_loader >> 4) E and F will be reserved:
 > 
 > 	E - extended IDs
 > 	F - special uses
 > 
 >    F is consistent with the current use of FF for "unknown".
 > 
 > - If the boot loader ID is E, the current pad1 field at 0x226 is 
 > repurposed as an extended loader ID.  The reason to use the pad1 field 
 > is that it is present in all headers since version 2.02.  The boot 
 > loader ID will simply be: ((extended ID + 0x10) << 4) + (version), where 
 > (version) as before is (type_of_loader & 15).  This is the value which 
 > will be reported in /proc/sys/kernel/bootloader_type.
 > 
 > The biggest question is probably: is there a need/desire for an extended 
 > version field, or is four bits enough for existing bootloader needs?

Why do we need a boot loader id at all? The purpose of a boot loader,
whatever it may be, is to load the kernel according to certain protocols.
Once that's done, why would the kernel care who/what loaded it?
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